The field of this invention relates to an improved method for the direct vapor-phase oxidation of aromatic aldehydes to phenolic compounds.
The direct vapor-phase oxidation of benzaldehyde to phenol is known. U.S. Pat. No. 3,850,995 to Horlenko et al. teaches the vapor phase preparation of phenol from benzaldehyde by reacting benzaldehyde with oxygen at a temperature of 250.degree. to 450.degree. C. According to the patentee, excessive amounts of tar were found to occur unless precautions were taken. Methods of alleviating the formation of tars and carbonaceous compounds concerned the use of a hydrocarbon diluent such as benzene and toluene.
The disadvantages of using a hydrocarbon diluent are: (1) in a diluted reaction regime, a larger residence time is required as compared to an undiluted regime to produce a given amount of product, (2) the unreacted hydrocarbon diluent must be separated from the product at the completion of the reaction. This separation entails an extra processing step.
We have found that the operating difficulties caused by the formation of tars and carbonaceous materials can be avoided by the process of our invention, i.e., (1) the method and temperature of mixing the reactant aromatic aldehyde with an oxygen-containing gas, (2) the temperature and residence time of the reactants in the reactor and (3) the method and temperature of the reaction quench following the reaction. A hydrocarbon diluent is not necessary.
It is, therefore, an object of the present invention to provide a method of converting an aromatic aldehyde to the corresponding phenolic compound in high yield without the necessity of using a hydrocarbon diluent. It is another object to provide an economical method for accomplishing such conversion over present methods by reducing formation of benzoic acid and by eliminating the need for separating a hydrocarbon diluent from product. Other objects of the invention will be apparent from the following detailed description and examples.